8 Categories of Radiation Dosimeters for Dose and Exposure Monitoring and Worker Safety

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Dosimeter Equipment Category

Description

Advantages and Disadvantages

Handheld survey meters

Examples:

Pancake Geiger - Mueller detector 1
  • Detect  surface contamination in the environment and on people
  • Low range: operate up to at least 10 mR per hour
  • High range: designed to operate up to 1000 R per hour

Advantages:

  • These meters have long been used for regulatory compliance of radiological or nuclear facilities.
  • Occupational workers are very familiar with their use.

Limitations:

  • Requires training to understand the option to display  more than one scale of units, AND which probe to use.

Personal dosimeter

Examples:

finger ring dosimeter
  • Small radiation monitor that is worn by an individual
  • Passively assesses accumulated personal dose equivalent
  • Usually processed outside the workplace after dose has been accumulated
  • Common individual dosimeters contain film, TLD,OSL, or direct-ion storage as the radiation detector

Advantages:

  • Can record personal dose equivalent very accurately, at the position where it is worn 
  • Some OSL dosimeters can be read using portable equipment, allowing readings in the field immediately after exiting the Hot Zone and before next mission assignment.

Limitations:

  • Only records accumulated exposures. Because it lacks real time display or alarm, it CANNOT prospectively help responders avoid dose of concern.

Pocket ionization chamber

Examples: in photo below older versions on top, newer version on bottom of photo below

pocket ionizing chamber

  • Small, strong, simple device worn by an individual 
  • To read dose, look through device to see deflection of needle
  • Typically the size of a large writing pen
  • Options for monitoring various exposure ranges
  • Other names: quartz-fiber dosimeter, self-indicating pocket dosimeter, self-reading pocket dosimeter

Advantages:

  • Can be read in the field in real time so user can avoid dose of concern
  • Minimal maintenance  
  • Can operate without batteries

Limitations: 

  • Does not alarm
  • Must be charged before use 
  • All dose readings must be recorded at the end of the single work period as device does not retain a record of the exposure
  • Can be difficult to read in the field, especially if user wearing respiratory PPE
  • May provide false reading if mechanically shocked 
  • Must match specific device selected with possible dose range from exposure  to protect wearer safety

Electronic personal dosimeter (EPD)

Examples:

Thermal electronic personal dosimeter

  • High range, alarming, active dosimeter, designed to be worn by occupational radiation workers in planned exposure situations, to measure personal dose equivalence for regulatory compliance, typically in industrial and medical settings
  • Displays dose AND dose rate
  • Some will alarm if either preset  threshold is exceeded
  • Typically use semiconductor detectors such as metal-oxide semiconductor field-effect transistor

Advantages:

  • Provides immediate information and alarm functions to help control exposure
  • Can function like a survey meter when displaying dose rate

Limitations:

  • Some devices not suited for tough emergency response conditions
  • Some lack large displays, or loud enough alarm noise or strong enough vibration alarms
  • Because they are used for regulatory confirmation of occupational worker dose, ANSI standard requires that the user be unable to change key alarm and dose parameters that would make them more useful in an emergency response situation.
  • Standard requires measures up to dose rate of  100 rem per hour (1 Sv per hour) dose limit of 100 rem (1 Sv per hour), but some devices exceed this.

Personal emergency radiation detectors (PERDs) and monitors

Examples:

personal emergency radiation detector

  • An alarming personal radiation detector worn on the body to detect photons and alarm if preset thresholds for either exposure rate or accumulated dose are exceeded.      
  • Designed to be used in harsh environments, with high exposure rates (>10 R per hour) for emergency response applications.
  • Appropriate device for responder dose monitoring and control

Advantages

  • Is the preferred tool for responders because the device ranges allow use multiple response zones: Cold Zone, Hot Zone, and Dangerous-radiation Zone
  • Accuracy the same as EPD but the higher dose rate range [0.001 to 999 R per hour (~10 micro Gy per hour to ~10 Gy per hour)] ensures that the device will NOT be saturated in an emergency exposure situation.
  • Ruggedly engineered, with robust vibration and sound alarm thresholds adequate for emergency situations
  • Monitors are similar to detectors but may not meet certain ANSI standards for extended range or durability

Limitations

  • ANSI standard for PERDs only requires an effective dose-rate range down to 1 mR per hour (1 micro Gy per hour) which may limit their use in the cold zone, although many devices have a larger effective range.

Non-alarming PERDs

Examples: SIRAD® (Self-indicating Instant Radiation Alert Dosimeters)

SIRAD® (Self-indicating Instant Radiation Alert Dosimeters)
(JP Laboratories, Inc)
  • Typically a colorimetric card with a sensitive area that darkens or changes color with increasing dose from exposure
  • Provides a visual indication of exposure to the user
  • Designed to be worn or carried on user's body
  • Does NOT have an active alarm

Advantages

  • Provide a visual indication of whether or not safety levels have been reached or exceeded, making them an appropriate back-up safety system to active monitoring with an alarm
  • Size of credit card, inexpensive, safe, robust in harsh circumstances

Limitations

  • Not very sensitive and generally cannot demonstrate exposure below 1 rem (10 mSV)
  • Does NOT alarm
  • Cannot alert the worker of hazardous conditions
  • May be difficult to interpret

Personal radiation detectors (PRDs)

Examples:

personal radiation detector

  • Similar in appearance to electronic dosimeters
  • Used to detect low levels of radiation for law-enforcement activities
  • Developed to help find and interdict potential radiological or nuclear terrorism threats  and identify radioactive material out of regulatory control
  • Primarily used by law-enforcement agencies

Advantages

  • Can alert the wearer to any unexpected, low levels of nearby radiation, including levels near background
  • Potentially useful during emergency response for activities OUTSIDE the Hot Zone

Limitations

  • ANSI standard for this device does not have a requirement for tracking integrated exposure over time, although some manufacturers add this option.
  • ANSI standard only requires an exposure rate range up to 2mR per hour (~20 micro Gy per hour), which is a low range; therefore, these devices often "saturate" a relatively low radiation levels and cannot be used in the higher dose response zones such as the Hot Zone or Dangerous-radiation Zone.

Extended range personal radiation detectors (ER-PRDs)

Examples:

extended range personal radiation detector

  • PRD with dual detector system that allows PRD to have an extended (high) dose-rate range without sacrificing the low dose-rate sensitivity
  • In addition to sensitive crystal or plastic scintillators, these devices may have a second, less sensitive detector such as a small G-M or solid-state detector

Advantages

  • If the ER-PRD is designed to track exposure rate AND total exposure during wear time, it would be appropriate for responder protection and monitoring in the Hot Zone.
  • If the device can support exposure rates up to 500 R per hour (~5 Gy per hour), it would be appropriate for the Dangerous-radiation Zone.
  • This could be a reasonable tool for both general public safety and security applications.
  • Limitations

    • Alarm set points must be changed to match the needs of the mission or task
    • Alarms set points for PRD use (low dose end), would not be appropriate for emergency response operations when dose from exposure could be in higher ranges.

    Radioisotope identification device (RIID)

    Examples:

    Radioisotope identifiation device

    • Developed to help search for and identify radioactive material in the field using gamma-ray spectroscopy
    • Used by law-enforcement and HAZMAT agencies.
    • For the Preventive Rad/Nuke Detection mission, hand held RIIDs can be used either as the primary search (detection) device to survey pedestrians, packages, cargo and motor vehicles for contraband material OR as a secondary search device for verifying and characterizing alarms from fixed detectors or PRDs.
    • For the public safety mission, RIID's ability to identify the radionuclide can help inform proper response protocols and safety considerations.
    • These devices require high quality scintillator or solid-sate detectors to discriminate different gamma-ray energies, detectors such as HPGe, NaI(TI), etc.
    • Complex, expensive devices

    Advantages

    • Can alert the wearer to any unexpected, low levels of nearby radiation
    • Useful in emergency response operations OUTSIDE the Hot Zone
    • Identifying the detected radionuclide could help determine if any altered controls (dose or dose rate or PPE) are needed for responder safety.
    • Can be programmed to provide dose estimates

    Limitations

    • ANSI standard does NOT require ability to track integrated (accumulated) dose from exposure, although some devices have this capacity
    • ANSI standard only requires an exposure rate range up to 2 mR per hour (~20 microGy per hour), a low dose rate. Therefore, with this sensitivity, these devices often "saturate" at relatively low radiation levels, making them NOT useful in the Hot Zone or Dangerous-radiation Zone.

    Source: Table above adapted from 2 documents:

    Abbreviations: R = roentgens; Gy =  gray ; Sv = sieverts
    TLD: thermo luminsecent dosimeter; OSL: optically stimulated luminescence
    ANSI Standard  - American National Standards Institute

    Radiation emergency worker: those who would be called upon to assist with the response to a radiation incident even though their regular job does NOT expose them to levels of radiation higher than normal background radiation

    Traditional radiation workers: those whose occupations involve exposure to radiation and who are part of an occupational radiation dose monitoring and protection program


    Radiation Zones are defined by the measurement of R in air at the perimeter of a zone; it could be "hotter" inside the perimeter line. isodose maps are created, and they are similar to maps with isobars or isotherms. See REMM graphic. This graphic relates to fallout after an IND but these zones could be defined in other kinds of incidents.


    Outdoor Radiation Zones as defined by  NCRP: Dangerous Radiation Zone: >10 R/h (>0.1 Sv/h); Hot zone >10 mR/h (>0.1 mSv/h);  Cold zone:  < 10 mR/h (<0.1 mSv/h) beyond this perimeter. Other organizations have different names for these radiation zones, as noted on REMM: